Several recent studies have suggested that tau protein, a microtubule associated protein found primarily in neuronal cells, has other functions beyond promoting the assembly and stabilization of microtubules. Since tau protein has been shown to accumulate pathologically in Alzheimer's disease brain, understanding its full functional capabilities will allow a better vantage point from which to analyze the disease state. Preliminary data obtained from a yeast two hybrid system has identified a new protein that interacts with tau. This protein also associated with actin filaments in 3T3 cells. In addition, the sequence of the protein corresponded to that of eed, a classical mouse developmental mutant. Tau and eed may link the microtubule and microfilament cytoskeletons and provide proper cytoskeletal organization in areas such as the growth cone. Specific Aim I investigates the interaction between tau, eed, actin and microtubules in vitro and in transfected cells. Binding affinities and binding sites will be determined using in vitro binding assays and transfected cells will be investigated using co-immunoprecipitation and immunofluorescence microscopy. Specific Aim II investigates the spatial and temporal expression of eed at the mRNA and protein levels. Antibodies specific for eed will be prepared and used on immunoblots and transfected neuronal cell lines. Northern blots will then be used to examine RNA. Specific Aim III investigates the interaction between endogenous tau and eed in neuronal cells using co-immunoprecipitation and immunofluorescence microscopy. This proposal will shed light on a new interaction that connects tau with the actin cytoskeleton. It also advances our knowledge on eed, a newly discovered protein.